High speed stress plane material pulverizer



July 27, 1965 H. G. KROHNE HIGH SPEED STRESS PLANE MATERIAL PULVERIZER 2 Sheets-Sheet 1 Filed June 15, 1962 INVENTOR HANS G. KROHNE BY M 2 4; ATTORNEY July 27, 1965 KRQHNE 3,197,147

HIGH SPEED STRESS PLANE MATERIAL PULVERIZER Filed June 15, 1962 2 Sheets-Sheet 2 FIG. 9 FIG. IO 7 76 76 70 5 w 74 ill I i i/ I l 2 7 INVENTOR HANS e. KROHNE BY KL.

ATI'ORNEY Unitcd States Patent 3,197,147 HIGH SPEED STRESS PLANE MATERIAL PULVERIZER Hans G. Krohne, Richmond, Va., assignor to American Machine 8; Foundry Company, a corporation of New Jersey Filed June 15, 1962, Ser. No. 202,849 17 Claims. (Cl. 241-227) This invention is an improved high speed pulverizer.

An object of the invention is the improvement of high speed pulverizers.

The pulverizing of materials has long been carried out by grinding. More recently a method was devised for reducing material to powders of any desired degree of fineness by cutting rather than grinding. In this method of pulverization, a mechanism well known as a microtome has been changed and adapted to perform the pulverizing function. A microtome is ordinarily a single disc-shaped rotor, with a small knife protruding from its outer edge, secured to a rotatable axis driven at high speed. One theory of the operation of the microtome is that the speed at which the cutting edge travels is so great that a layer of air is produced between the blade and the material upon which it acts which exerts such pressure on the material that the material is severed by a stress plane set up in the material by the pressure, without actual contact between the blade and the material. The cutting effected by the microtome, therefore, is known as stress plane cutting. Microtomes have been used generally for the cutting of very thin sections, as of organic tissue, for microscopic examination. Recently it was suggested that it might be possible to shred tobacco, for instance, by mounting a plurality of cutting elements on a single axis rotating at high speed. The cutting elements, hereinafter attimes termed blades, discs or knives, were spaced one from another at a distance equal to the desired width of shreds. The length of shred was controlled by providing material at the input to the blades of predetermined lengths. It was intended that the tobacco leaf, precut to a desired size, should make but a single pass through the blades. The machine was designed so that the total material was to make but a single pass through the blades and the results were found to be generally satisfactory. The machine, however, was provided with a housing which closely confined the rotating blades. It was found that this created a problem in that a small percentage of the material became entrained in the air stream between the multiple blades and the housing and was subjected to multiple divisions, resulting in a certain small percentage of particles of a wide range of fineness in addition to the shredded bulk of the material. It was then discovered that if ejection of any of the material were prevented, by blocking the normal means of egress from the machine, all of the material was pulverized in a very short time ranging from a fraction of a second to a few seconds at most, depending upon the material and the fineness desired. This stimulated interest in a practical machine, using the stress plane principle, which machine would be useful in speedily pulverizing any material, which was susceptible to pulverization.

There are advantages inherent in stress plane cutters which make them well adapted to pulverization. Since there is no actual contact between the material and the blades, because of the interposition of the air layer, and since it has been found that the air layer does not dull the blades, the blades will operate indefinitely without requiring resharpening. This appears true notwithstanding the material which is pulverized. Further, it is observable that in the case of vegetable matter, pulverizing may be performed with less loss of the natural juices as cutting does not depend upon contact with the blade. It is observable that in cutting materials generally, even in cutting most vegetable material susceptible to pulverization, there is no accumulation of juices or gums on the blades and no deposit of juices in or on the machine. This greatly minimizes the cleaning problem. The blades, which preferably are projections integral with the rotor, barring malfunction practically never require resharpening and rarely require cleaning. The problem of cleaning other parts of the machine is greatly minimized. This is an important advantage in the use of stress plane cutters, because of the inordinate time lost in the use of other types of cutters, in resharpening or replacing blades, and in the maintenance of the machines of which they form a part. a g

A pulverizer of the stress plane type should preferably be continuous in operation. One reason forthis is that the housing preferably encloses the blades snugly, tending to minimize the space available for the material in the cutting region of the machine. This is compensated, however, .by the speed with which the material is re duced. Another problem is control over the number of cuttings to which the material. is subjected. This is important in cases where uniformity in the size of the material particles is required. The present invention improves known stress plane pulverizers in affording a machine better adapted to produce uniformly sized particles of any predetermined fineness. Further the present invention'p'rovides a pulverizing machine operating on the stress plane principle which is better adapted to continuous operation than any such known machine.

Another object of the invention is improved control over the cutting operation in a multiblade high speed stress p'lanel pulverizer, to promote. uniformity in the size of the particles produced."

Another object of the invention is the production of a high speed stress'plane pulven'zer which is better adapted to continuous operation.

A featureof the invention is a stress plane pulverizer in which the cutting element takes the form of a helical, screw-thread-like projection on the periphery'of a high speed rotor. g

Another feature of the invention is a stress plane pulverizer provided with an input near one axial end of the high speed helical cutting blade and an output near its other axial end in which the movement of the material through the pulverizer is under control'of thelielical blade.

Another fe-atureof the invention is a stress plane pulverizer having a high speed rotor arranged with cutting elements in the form of multiple peripheral screw-threadlike projections.

verizer having a coacting pair of cutters, in the form of rotors on parallel longitudinal axes, each rotor being provided with a cutting element in the form of a helical screw-thread-like projection one of the thread-like projections having a right-hand pitch .and the other having a left-hand pitch and in which the two rotors are actuated in opposite senses.

Another feature of the invention is an outlet in a stress plane pulverizer, a dimension of which is adjustable in the direction of flow of the material, so that the number of divisions to which the material is subjected before it is ejected may be controlled.

.Another feature of the invention is a stress plane pulverizer having a pair .of coacting rotor cutting elements driven at different speeds.

These and other features of the invention may be understood from the following description and claims when read with reference to the associated drawings which taken together disclose preferred embodiments in which the invention is presently incorporated. The invention is not limited to incorporation in the described embodiments but may take other forms which may be suggested to those skilled in the art by the present di's closure. i

In the drawings:

lFIG. .1 is a vertical section through the machine taken at its central transverse position; a

FIG. 2 is a horizontal section;

FIG. 3 is a section takenthrough line 3-3 of FIG. 1

FIG; 4 is a section taken through line 4-4 of FIG. 1;

FIG..5 shows four different rotor tooth-shapes as seen till a partial longitudinal section through the axisof rota- 'tion of the rotors in the various figures;

FIG. 6 shows three ditferent rotor tooth arrangements;

FIG. 7 shows a vertical section of la modified form of the pulverizer of FIGS. 1, 2, 3 and 4 to provide an outlet which is adjustable in size in the direction in which the material is driven;

FIG. 8 shows another embodiment of the invention in vertical elevation;

FIG. 9 shows a vertical section and FIG. 10 shows a horizontal section of another embodiment of the in,- vention featuring conical rotors; I

FIG. 11 shows a vertical section and FIG, 12 shows a horizontal section of another embodiment of the invention having two cylindrical rotors mounted on axis which diverge from the parallel and having a housing spaced irregularly from the rotors. j

7 Refer now to FIGS. -1, 2, 3 and 4. V

The pulverizer comprises a housing in which are rotatably mounted two rotors 22 and 24, the shafts 25 and 27 'of which project through each end of the housing and are supported therein in bearings suitable for speeds ranging between 20,000 and 60,000 revolutions per minute. Th'e'diameters of the rotors may be selected so that the peripheral speed of the knives is between 300 and 700 feet per second. Shafts 25 and 27, as seen in FIG. l,-are each suitablycoupled to an individual motor 19 land 29, respectively. The rotors are 'provided on their cylindrical peripheries with screw-thread-like projections. These projections may be of many different shapes and sizes. They are indicated schematically on the peripheries .of the rotors of the various figures hereon as narrow thread like filaments. Actually they may take many forms, as explained hereinafter with reference to FIG. 5. The projection on one of the rotors 22 may havea left-hand pitch, for instance, and the projection on the other of the rotors 24 may have a right-hand pitch,

for instanceyor vice versa- Actually, the rotors, as

shown in FIG. 2, are connectedto motors 19 and 29 so that rotor .22 is driven clockwise and rotor 24 counterclockwise. The rotors are disposed in the housing in such manner that they are closely confined therein and so that their projecting knives engage each other closely without touching. It has been found advantageous to have the helical knife of one rotor spaced radially very closely to the helical knife of the other. However, when helical knives are employed, as in'the present invention, there should be no intermeshing of the knives. The housing is provided near one end, as seen in FIG. 1, with an inlet 26 and near its other end, as seen in FIG. 1, with an outlet 28. The material to be pulverized enters through the inlet. The rotors are of such size that the linear speed of the thread-like projections on their periphery, as mentioned, is between 300 and 700 feet per second. This speed is such that the material which is introduced is severed without actual contact with the blades. A theory has been proposed that the blades when rotating at their high speed in close proximity with the material create a layer of air, or gas, in the region closely adjacent the blades. This, it is considered, in turn, creates a high pressure which acts on the material and severs it by producing a stress plane within the material. It is believed that there is no actual contact between the blade-s .and the material. As a result of this, the blades do not require resharpening. Further, in cutting materials susceptible to pulverizat-ion, no juices or gums or other residue isdep-osit-ed on the blades or on other parts of the mechanism. As a result of this, the machine may remain in operation indefinitely without being required to be shut down for resharpening the blades or for recleaning .them or other parts of the machine.

An important advantage of the present machine is that the particles of material pass through the machine in substantially the same interval and are subjected to substantially the same amount of division. This is attributable to the arrangement of the rotor threads or blades, one having a left-hand pitchand the other a right-hand pitch and one rotor opera-ting clockwise and the other counterclockwise.

FIG; 5 shows four different rotor tooth shapes, A, B, C and D in longitudinal cross section, which are representative of a multitude of shapes which may be found satisfactory for use in pulverizers, dependent upon the material to be pulverized and the degree of fineness desired. Shape A is in the form of an isosceles triangle. Shape B is in the form of a right-angle triangle. Shape C is in the form of a rectangle. Shape D is in the form of the rectangle surmounted by a half-circular segment. The dimensions of the teeth, that is to say, their pitch and their height, may vary over a considerable range depending on the particular application.

Refer now to FIG. 6 which shows three different rotor tooth arrangements designated E, F and G. It is to be understood that the shape of the teeth in each one of these arrangements may be in accordance with any of the shapes A, B, C or D or any other shape found to be suitable. The rotor tooth arrangement shown in E is a single thread. The teeth in the F arrangement are multiple thread teeth. Instead of a single thread, there may be 1, 2, 3, 4 or more threads. In the F arrangement, a multiple thread having four helices is shown. In the G arrangement, the thread has a variable pitch. In this figms, the left-hand end is considered to be the input end of the pulverizer. At this ends, the pitch is widest and gradually reduced in the direction of progress toward the right or output end.

Refer now to FIG. 7. The embodiment, in accordance with FIG. '7, differs from that in accordance with FIGS. 1, 2, 3 and 4 in that in FIG. 7 an outlet is provided, the dimension of which in the direction of movement of the material from the input to the output is adjustable. In FIG. 7, a central section of the bottom is provided with an adjustable slide having a horizontal portion 30 terminating in a vertical portion 32. The slide is adjustable so that the spacing 31 between the vertical element 32 and the right-hand end wall 34 of the pulverizer may be changed as desired so that the distance through which the material moves between the input of the pulverizer and its output may be shortened as desire-d to control the amount of division to which the material is subjected. This slide may be arranged so that the material is subjected to as wide a range of comminution as may be de sired. When the vertical element 32 is moved to the extreme left-hand position, the material is ejected after being subjected to the pulverizing process for only a relatively small percentage of its full range. As the vertical projection 32 is adjusted more closely to the right-hand end wall 34 of the machine in FIG. 7, the material is subjected to a larger percentage of the total possible pulverizetion of the machine.

'Refer now to FIG. 8 which shows yet another embodiment of the invention. In this arrangement, a motor 40.

is provided with a driving pulley 42 which is connected by means of a continuous belt 44 to the pulley 46 mounted on the end of one of the two rotors and to the pulley 48 mounted on the end of the second rotor in the pulverizer. Pulleys 46 and 48 may be made to have any desired ratio of diameters. As shown in FIG. 8, pulley 48 is considerably smaller than pulley 46 and, therefore, drives its associated rotor at a faster rate than pulley 46 drives its associated rotor. As a result of this, the threads of the two rotors, relative one to another, progress with different speeds between the input and output of the pulverizer. This has been found to improve the pulverizing action for certain applications; The pulverizer in FIG. v 8 is equipped with a conventional pneumatic pick-up system comprising a cyclone 50 connected by means of a tube 52 to the output 54 of the pulverizer and to an air inlet 56. In this arrangement, the pulverized material passes through duct 54 into tube 52 through which it is transported by the air received through inlet 56. The material ultimately passes through gate 58 into container 60.

FIGS. 9 and 10, taken together, show another embodiment in which a helical knife, or helical knives, are formed on the curved surfaces of two rotors, 70 and 72, each of which is in the form of the frustum of a cone, the longitudinal axes of which are parallel. The material is introduced near the end where the cross-sections of the cones are smaller and is impelled toward the end where the crosssections of the cones are larger. As a result of this construction, the space 74, near the input, is larger than in the embodiment of FIGS. 1 and 2. The casing 76 may conform closely to the outer conical surfaces but preferably is parallel to the axis of the rotors as shown. In this arrangement, the space surrounding the rotors is reduced in the direction of motion of the material.

FIGS. 11 and 12, taken together, show another embodiment of the invention in which the rotors are cylindrical but are mounted on axes which diverge from parallel and in which the housing 84 is in the form of a curved surface, which is concave, bending slightly inwardly from an enlarged end 81 toward a smaller end 83, where it conforms closely to the rotor. This affords enlarged spaces, such as 85 and 87, near the input of the pulverizer.

What is claimed is:

1. A pulverizer having a rotor, a material pulverizing element on said rotor, said element having a helical, or screw-thread-like, projection formed on the periphery of said rotor, a casing snugly enclosing said projection and means for driving said element at a circumferential speed of more than 300 feet per second to pulverize material.

2. A stress plane pulverizer having a rotor, a casing snugly conforming to said rotor, an input near one axial end of said rotor, an output near the other axial end of said rotor, a helical cutting element on said rotor, for impelling material between said input and said output and means for driving said element at a linear speed in excess of 300 feet per second to pulverize material between said element and said casing.

3. A stress plane pulverizer comprising a cylindrical rotor having a cutting and material propelling projection threaded helically on its cylindrical surface, means for driving said projection at a linear speed in excess of 300 feet per second, a casing coacting with said projection in comminuting material, said casing closely confining said projection, said casing having an input and an output, said input fixed near one axial end of said rotor, said output having a dimension adjustable with respect to the opposite end of said rotor, so as to control the amount of pulverization by controlling the length of travel of material between said input and said output.

4. A stress plane material pulverizer comprising a housing, an elongated rotor having a cylindrical surface, an elongated helical knife, concentric with said axis, extending the length of said surface, said knife spaced close to said housing, means for actuating said knife at a linear speed in excess of 300 feet per second to create a stress plane in said material, means for actuating said knife continuously and means for controlling the amount of comminution to which said material is subjected in said pulverizer. a

5. A stress plane material pulverizer comprising a rotor, a helical knife, integral with said rotor, extending axially on the periphery of said rotor, for comminuting and propelling saidmaterial, means for actuating said knife at a speed in excess of 300 linear feet per second, a housing snugly enclosing said knife, an input in said housing, near one end of said rotor, and an output in said housing, spaced from said input, in the direction of the axis of rotation .of said rotor, said output having a dimension parallel to said axis and means for varying said dimension, to control the amount of comminution to which said material is subjected by the effect of air pressure produced by the speed of said knife, during the interval while said material is propelled by said knife between said input and said output.

6. A stress plane material pulverizer comprising. an input, an output and a rotor, said rotor having a helical knife extending axially of its periphery between said input and said output, the pitch of said helix being greater near said input than near said output, a housing enclosing said knife and spaced relatively closely therefrom, and means for actuating said knife at a speed in excess of 300-linear feet per second, so. as to pulverize said material by the effect of air pressure produced in the confined space between said'knife and said housing.

7. A continuous combined stress plane material pulverizer and material impeller comprising a housing, two rotors mounted on parallel axes within said housing, a helical knife on the cylindrical periphery of each of said rotors, said rotors disposed within said housing so that said helical knives are in very close radial proximity, said rotors rotatable in opposite senses at such a speed that said knives have a circumferential speed greater than three hundred feet per second, said housing fitting snugly about said knives so as to coact with said knives in pulverizing said material, due to the pressure of air set up by said speed of rotation of said knives and exerted upon said material in the confined space between said knives and said housing and between one and the other of said knives, an input, centered between said rotors, near one axial end of said rotors, an output centered between said rotors near the other axial end of said rotors, the direction of rotation of said knives being such as to impel said material continuously from said input through said output, to increase the output of said material.

8. A continuous combined stress plane material pulverizer and material impeller in accordance with claim 7 in which the cross sectional area of said output may be varied by changing a dimension in the direction parallel to the axes of rotation of said rotors to control the fineness of pulverization of said material. 9. A continuous combined stress plane material pulverlzer and material impeller in accordance with claim 7 in which said helical knife on one of said rotors has a righthand pitch and said helical knife on the other of said rotors has a left-hand pitch to promote the movement of material.

10. A continuous combined stress plane material pulverizer and material impeller in accordance with claim 7 in which one of said rotors has a plurality of helical knives arranged as multiple threads.

11. A continuous combined stress plane material pulverizer and material impeller in accordance with claim 7 in which one of said rotors has a helical knife, the pitch of which helix varies, being greater near said input.

12. A continuous combined stress plane material pulverizer and material impeller in accordance with claim 7 having a fir t means for driving one of said rotors at a first rate and a second means for driving the other of said rotors at a second rate, different from said first rate.

verizer and material impeller in accordance with claim 7 in which the cross section of said helical knife is rectangular to increase its strength.

14. A continuous combined stress plane material pul verizer and material impeller in accordance with claim 7 in which the longitudinal cross section of said helical knife is a rectangle surmounted by an integral semicircular segment, to minimize breakage by eliminating pointed projections.

15. A continuous combined stress plane material pulverizer and material impeller, comprising a pair of rotors in the form of right conical frustums having their longitu dinal axes horizontal and fixedly parallel, said rotors enclosed in a common housing, an elongated pulverizing and impelling projection on the cylindrical surface of each of said rotors, said projection extending helically in the direction of the axis of rotation of its respective rotor, and means for actuating said' projections at such high speed as to pulverize the material by air under pressure, produced by the high rotational speed of said projections.

16. A continuous combined material stress plane pulverizer and material conveyor comprising ,a pair of right cylindrical rotors having their longitudinal axes disposed in fixedly horizontal and, non-parallel relationship, said rotors enclosed in a common housing, an'elongated projeetion extending helically along the surface of each of said rotors in the direction of its respective'axis of rotation, means for actuating said projections at such a speed as to pulverize material by the action of air due to the speed of movement of said projection.

17. A combined stress plane material pulverizer and material impeller comprising a cylindrical rotor enclosed in a housing, an input and an output in said housing,

said housing having cross sections diminishing in area in a direction parallel to the axis of said rotor between said input and said output, said rotor having helical projections thereon or pulverizing and impelling said material and means for actuating said projections at such a speed as to pulverize material by the action of air due to the speed of said projections.

References Cited by the Examiner UNITED STATES PATENTS 155,662 10/74 Meland 241235 X 461,789 10/91 Winchell 241-222 813,273 2/06 Bach 241235 X 996,958 7/11 Wallick 146183 1,420,742 6/22 Phillip 241-227 X 1,463,720 7/23 Negro 241293 X 1,465,941 8/23 Hill 146183 FOREIGN PATENTS 1,206,600 2/60 France.

234,842 6/09 Germany.

394,820 5/24 Germany.

693,190 6/53 Great Britain.

OTHER REFERENCES J. SPENCER OVERHOLSER, Primary Examiner.

EVERETT W. KIRBY, Examiner. 

1. A PULVERIZER HAVING A ROTOR, A MATERIAL PULVERIZING ELEMENT ON SAID ROTOR, SAID ELEMENT HAVING A HELICAL, OR SCREW-THREAD-LIKE, PROJECTION FORMED ON THE PERIPHERY OF SAID ROTOR, A CASING SNUGLY ENCLOSING SAID PROJECTION AND MEANS FOR DRIVING SAID ELEMENT AT A CIRCUMFERENTIAL SPEED OF MORE THAN 300 FEET PER SECOND TO PULVERIZE MATERIAL. 